Location filming in Cambridge and a studio session were completed but the strike nixed further work and the project was later shelved entirely for fear it might affect the Beeb's Christmas-time productions.

The remaining parts have been filled in with animation and the voice of 83-year-old Baker, although he also filmed a scene.

BBC Worldwide has now released the episodes, which interweave the 1979 footage with the new material to complete the story.

"I loved doing Doctor Who, it was life to me," Baker told the BBC of his tenure as the much-loved Time Lord. "I used to dread the end of rehearsal because then real life would impinge on me. Doctor Who... when I was in full flight, then I was happy."

"Shada" refers to a lost planet where the Time Lords built a prison for attempted universe conquerers.

In the ep, the villainous alien upstart Skagra requires the help of an inmate. However, no one knows the planet's location any more – except Professor Chronotis, a retired Time Lord trying to wind down in Cambridge.

Adams ended up using elements of the plot in his novel Dirk Gently's Holistic Detective Agency, where Chronotis is a university professor who happens to be hundreds of years old.

Alongside Baker, Lalla Ward plays The Doctor's companion, Romana, and the original Tardis, as it appeared in 1979, also features in the new scene.

It's not Baker's first revisit to the cult sci-fi series either. In 2013's Day of the Doctor, he made a guest appearance as "The Curator".